Ive seen my fuel light like twice. Both times i could barely squeeze 11 gallons in it. Damn inacurate fuel guage. I usualy fill up about 240 or so on the trip meter. Thats usualy below the 1/4 of a tank on the gauge. I usualy average like 24~26 in city(automatic) and over 30 on the highway...then that one time where i got almost 40 or some weird **** like that. Drove Elizabethton to Nashville stoping in Cookeville, thats like ~300 miles, and could get like 8 or 9 gallons in dont remember how much exactly, its in the car tho. its done that like twice. So who knows...
If you are getting mid 20's i would check everything, maybe o2 sensor. But go for a long highway drive see what you get. And dont go by the gauge just watch your trip meter when you get around 240 you should gas up, you should be around 1/4 tank sometimes high sometimes low. then divide mileage by gallons put in.